The present invention relates to a method of manufacturing a folded-fin heat sink assembly, using laser welding to tack a folded-fin assembly to a base, core or other heat-absorbing mass prior to brazing, and to apparatus for carrying out the method.
Folded-fin heat sinks are intended for use as active or passive heat sinks for microprocessor packages. Over the years, power used by microprocessors has increased considerably, and consequently, so has the heat generated by these devices. In order to provide adequate cooling, heat sinks with greater cooling capacities have become essential. If adequate cooling is not provided, the devices may overheat, resulting in damage to the devices and/or a reduction in operating performance. As a general rule, the performance of integrated circuit devices improves when they are operating at lower temperatures. Hence more effective heat sinks are needed, to facilitate lower integrated circuit operating temperatures.
In addition to meeting cooling requirements, heat sinks must accommodate space limitations. They must therefore be as compact and efficient as possible. They must also be as light in weight as possible, and must be capable of being efficiently mass-produced.
Historically within the microprocessor industry, the majority of heat sink solutions have used aluminum extrusions, typically using aluminum alloys 6061 T6 (with a thermal conductivity of 167 W/mK), or 6063 T6 (with a thermal conductivity of 200 W/mK), for example. The surface area aspect ratio (i.e. the ratio of surface area to base area) is typically limited to a maximum of about 12:1 with such extrusions. However, the higher power microprocessors now on or coming into the market require more efficient and effective cooling than can be achieved with the old extrusions.
To provide this greater efficiency and effectiveness in cooling microprocessors, xe2x80x9cfolded-finxe2x80x9d heat sinks have become known recently. In most such heat sinks, a length of thin metal (normally aluminum or an aluminum alloy) is successively folded to produce fins extending upwardly from a high-thermal-conductivity base (normally copper or an aluminum alloy), the fins being integrally joined alternately by upper and lower web portions, the lower web portions being bonded to the base. The base in turn is mounted on top of the microprocessor package, to collect the heat therefrom. For an active heat sink, a fan is suitably mounted to draw or force air through channels between adjacent fins.
In some such heat sinks, referred to as radial designs, the folded-fin assembly is arranged around a cylindrical core, such that the fins extend radially outwardly from the core. In such designs, the xe2x80x9clowerxe2x80x9d (inner) webs are secured to the core rather than to a base. There is normally a separate base to which the core is bonded, or the core may be integrally formed with the base, or the bottom of the core may itself constitute the base which contacts the microprocessor or other heat-generating device.
A key difficulty in the prior art is being able to manufacture these folded-fin heat sink assemblies efficiently and with reliable quality control. In particular, in brazing, soldering or otherwise bonding the folded-fin assembly to the base, it is difficult to maintain proper alignment of the assembly and proper spacing of adjacent fins. In the usual design, the folded-fin assembly tends to float on the base, and there is an accordion-like tendency for the spacing between adjacent fins to float as well, with wicking tending to pull fins together. In a radial design, similar problems exist with positioning the folded-fin assembly on the core. These factors can affect performance, i.e. heat dissipation efficiency, as well as aesthetics of the product.
To some extent, this problem can be overcome by the use of suitable fixtures to hold the folded-fin assembly in place. However, this requires a greater capital outlay (i.e. for a significant volume of suitable fixtures), and also results in higher operating costs, principally the energy cost in the brazing furnace for heating not just the folded-fin and base, but also the fixtures.
For convenience, all references herein will be to brazing of the folded-fin assembly to the base, but it should be appreciated that the invention is applicable to any other form of bonding of the folded-fin assembly to the base. Also for convenience, most references will be to the xe2x80x9cusualxe2x80x9d design of the folded-fin assembly having its fins extending upwardly from a base, but it should be appreciated that the same principles will apply to radial designs.
It is an object of the invention to provide a method for improved manufacturing of folded-fin heat sink assemblies, and to provide suitable apparatus for carrying out that method.
Therefore the invention provides laser welding of the folded-fin assembly to the base (or core) at selected points, prior to brazing or otherwise bonding to the base (or core), to properly position the folded-fin assembly and to maintain proper spacing between adjacent fins. The welds are robust enough to prevent fins from floating on the liquidus interface created in the brazing process. After the laser welding, the assembly is brazed, to provide full contact between the web portions of the folded-fin assembly and the base or core.
In the preferred method and apparatus, finger elements are inserted between adjacent fins, to maintain proper spacing, and the folded-fin assembly is pressed against the base or core to ensure good contact, before laser welding.
In the preferred embodiment of the apparatus, there is a first station for loading components of the heat sink assembly into suitable fixturing, and a welding station where the laser welding is effected. Preferably, the stations are at different circumferential locations around a rotatable dial assembly. If desired, there can be a separate unload station between the welding station and the first station, and/or a second station between the first station and the welding station, where a finger tool is inserted in each folded-fin assembly, and each folded-fin assembly is then lifted the finger tool into position on the base.
Further features of the invention will be described or will become apparent in the course of the following detailed description.